The invention relates to a locking arrangement having a lock cylinder and a matching key; the key having a flat key bit with a narrow spine, two broad sides which run substantially parallel to one another, and coding notches on the front, which is opposite the spine, at coding positions on the key bit; the lock cylinder having a cylinder housing, a cylinder core which is mounted in a bearing hole in the cylinder housing and has a keyway for insertion of the key bit, tumblers which are located in core pin holes, interact with the coding notches on the key bit, and are disposed at coding positions on the cylinder, said coding positions coinciding with coding positions on the key bit when the locking bit is inserted as far as a stop in the keyway, and a sensing member which is located in a supplementary core hole that extends transversely relative to the core pin holes and senses a sensing point on a broad side of the key, the spacing, from the spine, of the sensing point on a broad side of the key being greater than the spacing, from the spine, of the apex of the coding notch that is cut-in to the deepest extent, the sensing point being situated close to a peripheral edge of a coding notch which is cut-in to a lesser extent than the coding notch that is cut-in to the deepest extent in such a way that deepening, of the coding notch which is cut-in to a lesser extent, to the depth of the coding notch that is cut-in to the deepest extent leads to disappearance of the sensing point. A locking arrangement of this kind is known from DE 27 38 313 C2.
The locking arrangement described there has core pins located in core holes, the core pins sensing the coding notches of a flat key. At the same axial level as one of the core pins, there are respective sensing members in supplementary core holes that run transverse to the core pin holes, the sensing members sensing the tip region of the core pins when the core pin enters the coding notch assigned to it. In the case of a key for which the notch depth of the coding notch is too small, the two sensing stub ends of the sensing member interact with a portion of the core pin of smaller diameter, so that they release blocking steps against which a housing pin engages when the cylinder core is rotated.
A further locking arrangement is described by U.S. Pat. No. 3,742,744. The key described in the document has a flat key bit, a narrow spine, a front which is opposite the spine, and two broad sides which run parallel to one another and are provided with profiled grooves and profiled ribs disposed between the profiled grooves. The key front is provided with a large number of coding notches cut-in to individual depths. Each of the coding notches has an apex. The apex is spaced from the spine of the locking bit. One of the apexes is at a minimum distance from the spine of the key bit. This is the coding notch that is cut-in to the deepest extent. The coding notches are spaced equally from one another and are situated at coding positions. The individual coding positions are equally spaced apart from one another. A sensing point, which is in the form of a recess and can be sensed by a supplementary tumbler pin that is mounted in a core hole, is also located on the broad side of the key. The distance by which the sensing point is spaced from the spine of the key corresponds substantially to the distance from the apex of the coding cutout that is cut-in to the deepest extent to the spine. The associated lock cylinder has a housing, a core which can be rotated in a bearing hole in the housing, and a large number of tumblers. The tumblers are located in core holes and housing holes and are in the form of pins which prevent the core from rotating when a key is not inserted. The tumbler pins are equally spaced apart from one another in the core, in the direction of extent of a keyway, and are positioned at coding positions. If the matching key is inserted into the keyway as far as a stop position, the coding positions of the key bit coincide with the coding positions of the lock core, so that the tips of the core pins engage in the coding notches.
A customary method of opening such lock cylinders is the so-called bump key method in which keys are used, the coding notches of which are cut-in to the maximum possible depth. In principle, it suffices, for a bump key, to deepen the coding notches to a depth which corresponds to the depth of the coding notch of the proper key that is cut-in to the deepest extent.